In the search for hydrocarbons and development of hydrocarbon-bearing wells, hydraulic fracturing is a common technique to improve hydrocarbon recovery. Hydraulic fracturing involves injecting a high-pressure fluid into a wellbore to create or expand cracks in the subsurface formations so that natural gas and petroleum can flow more freely. Sometimes proppants (e.g., sand or aluminum oxide) are added to the fracturing fluid and remain in the fractures to hold them open to some degree when the hydraulic pressure is reduced and thus improve fluid flow through the fractures.
It may be difficult to determine whether a fracture downhole is operating as intended or if a flow rate through a given perforation cluster is as expected without a significant interruption of downhole operations and use of expensive and time-consuming equipment. For example, deployment of a wireline logging tool to collect flow rate data would interrupt and/or delay other downhole operations. Even if more permanent installations of flow rate sensors downhole were possible, distributing multiple sensors in a way that effectively monitors flow near different perforation clusters would be costly and tedious.
Most wells are not instrumented with anything more than a surface and/or downhole pressure meter. Downhole flow estimation is highly uncertain when using only pressure data and a model of the reservoir. There are commercial downhole flowmeters available but they suffer from technical limitations regarding placement in the wellbore, orientation, and acceptable flow rates. During hydraulic fracturing, the flow rates are so large (50,000-70,000 barrels per day) that mechanical flow meters often do not survive, particularly when proppant is used.
Fiber optic sensing systems have been developed to monitor downhole parameters such as vibration, acoustics, pressure, and temperature. Unfortunately, efforts to correlate acoustic activity with fluid flow have thus far resulted in inaccurate estimates.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.